However, in reality there is not going to be a perfect shuffle. It's very likely that some of your cards will remain "clumped" with others during your shuffle. Between games this means certain cards that are meant to be together (evolutions for example) will remain together. Pile shuffling (or any means of de-clumping) reduces this effect.
While it is true that both pile shuffling and declumping reduces the chance of having certain cards played in the last game clumped together, they are certainly
not the same thing. When pile shuffling, you have
no knowledge of what cards you are holding, so you might as well "clump" two cards together. When declumping, you
have knowledge by looking at the cards, and you are
making sure that no two cards are clumped together, so it obviously is a lot less random than a pile shuffle.
I also believe that by doing enough riffle shuffles and/or overhand shuffles, you can achieve a degree of randomness that is close to "true" randomness. However, any kind of deliberate rearranging (such as declumping) in between "true" shuffles is effectively reducing this degree of randomness, and therefore I consider it cheating.
Further, I would argue the point of shuffling in TCG games is not randomness for the sake of randomness but so that each player does not know the order of cards in their deck. De-clumping increases this effect (if done blindly) because you cannot expect cards that were adjacent at the end of last game to be adjacent this game.
Therefore I believe blind de-clumping improves overrall gameplay. After all, it's better for a game to be decided by skill of the players (whether that be deck-building or tactical) and not by who got the better hand.
This part really upset me. If you cannot expect cards that were adjacent last game to be adjacent this game, you are
cheating. If declumping were allowed to the extent you are describing, so that you could "never get a bad hand", then it would be a completely different game. Variance is a part of the game - a newbie should be able to beat a pro if the pro draws really bad - but it's all about building your deck to minimize that variance. Declumping must not be a skill you have to master in order to beat the pros because then, it wouldn't take long until people resorted to true stacking.
In short, blind declumping might "improve" overall gameplay - by reducing the amounts of donks for example - but donks are a part of the game, whether you like it or not. If you hate them so much, build a deck with more basics or go play Magic instead, declumping is not the solution.